1. Finch beaks and the need for statistics
You are now carrying a well-stocked toolbox.
2. Your well-equipped toolbox
You know how to take a data set and explore it. You know how to think probabilistically and infer values and confidence intervals for parameters. And you know how to formulate a hypothesis and use your data, and Python, to test it. Let's put those tools to use! In this chapter, you will immerse yourself in what is in my opinion one of the most fascinating data sets out there. You may know that many of the important observations that
3. Image: Public domain, US
led Charles Darwin to develop the theory of evolution were made
4. Image: NASA
in the Galápagos archipelago, particularly in the study of the small birds, called finches, that inhabit them. The islands are ideal for studying evolution because they are isolated so they do not have complicated effects from interactions with other species including humans. Furthermore, some of them are small, so entire populations can be monitored on a given island. Every year since 1973, Peter and Rosemary Grant of Princeton University have been spending several months of the year on
5. The island of Daphne Major
the tiny volcanic cinder cone island of Daphne Major in the Galápagos.
6. The finches of Daphne Major
This island has two dominant ground finch species, Geospiza fortis and Geospiza scandens. The Grants have monitored them every year, tagging them, making physiological measurements, taking samples for genetic sequencing, and more. In 2014,
7. Our data source
they published a book entitled "40 Years of Evolution: Darwin's Finches on Daphne Major Island". They generously placed all of their data on the Dryad data repository making it free for anyone to use. The data set is impressive and a great set for using data science and statistical inference to learn about evolution. You will work with the Grants' measurements of
8. The dimensions of the finch beak
the beak length and
9. The dimensions of the finch beak
beak depth. You will consider different aspects of the beak geometry, including how it varies over time, from species to species, and from parents to offspring. I will come back with short discussions as you are working through the data sets, but you are mostly on your own. You can do it! Ok, for your first analysis,
10. Investigation of G. scandens beak depth
you will investigate how the beak depth of Geospiza scandens has changed over time. You will start with some exploratory analysis of the measurements of these species from 1975 and 2012. You will then perform a parameter estimation, with confidence intervals, of mean beak depth for those respective years. Finally, you will do a hypothesis test investigating if the mean beak depth has changed from 1975 to 2012.
11. Let's practice!
Have at it!